1. Field of the Invention
Aspects of the present invention relate to a reformer for a fuel cell and a fuel cell system including the same. More particularly, aspects of the present invention relate to a reformer having a simplified structure, excellent oxidation activity, and excellent oxidative selectivity.
2. Description of the Related Art
A fuel cell can be used in a power generation system to produce electrical energy through an electrochemical redox reaction of an oxidant and a fuel. A suitable fuel can be hydrogen, or a hydrocarbon-based material, such as methanol, ethanol, natural gas, and the like. Such a fuel cell is a clean energy source that can reduce the demand for fossil fuels. It includes a stack composed of unit cells, and produces various ranges of power output. Since it has a four to ten times higher energy density than a small lithium battery, it has been highlighted as a small portable power source.
Representative exemplary fuel cells include polymer electrolyte membrane fuel cells (PEMFC) and a direct oxidation fuel cells (DOFC). The direct oxidation fuel cells include direct methanol fuel cells that use methanol as a fuel.
The polymer electrolyte fuel cells have a high energy density and a high power output, but also have problems in that they use hydrogen gas as a fuel, which must be carefully handled. In addition, producing hydrogen gas often requires accessory facilities, such as fuel reforming processors for reforming methane, methanol, natural gas, and the like.
On the contrary, a direct oxidation fuel cell has lower energy density than that of a polymer electrolyte fuel cell, but is easier to handle, can operate at a lower operation temperature, and producing its fuel does not require additional fuel reforming processors.
In a fuel cell system, a stack, that includes several to scores of unit cells stacked adjacent to one another, generates electricity. Each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly is composed of an anode (also referred to as a “fuel electrode” or an “oxidation electrode”) and a cathode (also referred to as an “air electrode” or a “reduction electrode”) that are separated by a polymer electrolyte membrane.
A fuel is supplied to the anode and is adsorbed on catalysts of the anode, and the fuel is oxidized to produce protons and electrons. The electrons are transferred to the cathode via an external circuit, and the protons are transferred to the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode, and then the oxidant, the protons, and the electrons are reacted on catalysts of the cathode, to produce electricity along with water.
Generally, a fuel cell system is composed of a stack, a reformer, a fuel tank, and a fuel pump. The stack forms a body of the fuel cell system, and the fuel pump moves the fuel from the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen gas, and supplies the hydrogen gas to the stack.
A reformer generally includes a reforming reaction part that generates hydrogen gas from a fuel, through a catalyst reforming reaction, using heat energy. A fuel cell system generally includes a carbon monoxide reducing part that removes carbon monoxide from the hydrogen gas, through oxidizing reaction that promotes the oxidation of the carbon monoxide over the oxidation of the hydrogen gas. Such a reforming reaction is performed by a reforming catalyst, and therefore, there is currently much research into reforming catalysts.